Method of aromatizing hydrocarbons



Aug. '22, 1'944,

1 R F RUTHRUFF METHOD OF AROMATIZING HYDROCARBONS I Flled Apml 2s, 1938INVENTOR P0 rf, FPu/wff BY r TTORNEY SSS@ 1 Patented Aug. 22, 1944METHOD OF ARJOMATIZIN G HYDROOARBONS Robert F. Ruthruff, Nutley, N. J.,assignor to The M. W. Kellogg Company, New York, N. Y., a corporation ofDelaware Application April 23, 1938, Serial No. 203,886

3 Claims. (Cl. 260-668) My invention relates to a method of aromatizinghydrocarbons.

It is well known that for many applications petroleum naphthas and otherlight petroleum hydrocarbons of high aromatic content are desirable andnecessary; in fact only under the most unusual circumstances does thepresence of aromatics in petroleum naphthas limit their application. Ahigh aromatic content is desirable in high solvency naphthas employed inthe lacquer industry and the presence of compounds such as toluene andxylene is very benecial in aviation fuels. It has heretofore beenrecognized that aromatic hydrocarbons can be obtained by the thermaldecomposition of hydrocarbons, the aromatic content of the reactionproduct increasing normally with increased severity (i. e., lncreasingtemperature) of treatment. During the pyrolytic treatment ofhydrocarbons to produce aromatics unsaturated hydrocarbons areinvariably obtained as a by-product. In many applications the presenceof olens-in the aromaticrich naphtha is undesirable or in many casesprohibited. For example, aviation fuels should contain only a minoramount of oleiins, while in the case of high solvency naphthas thepresence of olens is altogether undesirable. Furthermore if thearomatics are to be used in chemical synthesis (e. g., sulphonation,nitration, or the like) olefns must be absent for obvious reasons.

Heretofore it has been suggested by investigators conducting researchalong these lines that oleflns be removed from the aromatic-richmixturesformed, for example, by the high temperature pyrolysis of hydrocarbons,by hydrogenation. 'I'his procedure will remove olens but it is veryunsatisfactory since unless the reaction is controlled with greataccuracy aromatics will also be hydrogenated. In addition, I have foundthat hydrogenation in such cases is not only unsatisfactory but is infact the antithesis of the propery mild hydrogenation or by other means.My invention may perhaps be best understood by illustrative examples.

For instance, a gas reversion naphtha having approximately the followingcomposition, was

treated in the process:

Per cent olefins 35 Aromatics v 25 Naphthenes Parains 25 This materialwas produced by cracking naphtha under high temperature and pressure inthe presence of the readily condensable gas formed in the reaction. Thect arge after passing through the cracking or reaction zone wasseparated by fractionation into cuts representing:

1. Methane, hydrogen and most of the Cz hydrocarbons 2. C3 and C4hydrocarbons 3. Gas reversion gasoline 4. Polymer The second cut wasrecycled and added to the naphtha-charge. Obviously, condensables froman extraneous source may be used to increasefthe amount of cut'#2 ifdesired. v l

By catalytically hydrogenating the above material under as mildconditions as possible consistent with complete olefin removal, `theresulting product would have approximately the following composition:

Percent Aromatics 15 Naphthenes 65 Paramns 20 From the above it isevident that by hydrogenation methods all of the oleiins and a largebeen hydrogenated Per cent Aromatics 70 Olens 10 Naphthenes 5 Paramns 15Subsequent to the above dehydrogenation there may be optionally used asecond step of mild hydrogenation in which the residual olens areremoved and la. final product obtained having the composition givenbelow:

In the dehydrogenation step I preferably employed a dehydrogenating ringclosing catalyst such as a chromium oxide deposited upon alumina as acarrier in the proportions of 10% chromium oxide to 90% alumina. As analternative method of operation a straight dehydrogenating catalyst maybe used such as metallic nickel deposited on pumice.

A second application of the process is the treatment of highly aromaticliquids produced by high temperature pyrolysis of gaseous or liquidhydrocarbons at sub-atmospheric to moderately high super-atmosphericpressures in the manufacture of commercial gas. It is conventionalpractice in the manufacture of gas to burn a fuel gas withtheoretical-air (controlled to produce a substantially neutralatmosphere during burning), and into thel combustion gases atomize aMid-Continent gas oil. The aromatic liquids are obtained in thisprocedure by fractionation and removal of relatively heavy bottoms andtherecovery of the aromatics to be treated by separation of frac-l tionstaken overhead. A liquid containing up to '70% aromatics or more isobtained in this manner. These fractions are in some cases adapted touse as solvents in the paint industry or 'for other purposes. From thevapors formed by taking 70% overhead and maintaining a top towertemperature of approximately 540 F. a liquid may be fractionated whichis highlyaromatic. Such a liquid is advantageously treated for itsimprovement and elimination of objectionable characteristics. Tests madeupon a, distillate produced in this way, the inspections on'which areshown in the rst column of Table I, those on a cut representing a 70%overhead fraction from this material being givenin the second column,will now be considered.

TABLE I Column No.

Stoclrm..` Total 70% OH Hyd. Dehyd.

p Dist. 70% OH 70% OH Gravity, "A. P. I 26. 3 34.1 35. 7 34. 8 A. S. T.M. Distillation:

Initial "F 152 145 174 113 Percent recovery. 96. 98. 5 98. 5 97. 5

Residue Coke 1. l 1. 2 1. 1

Loss 0.4 0. 3 1. 4 Percent Olens 90. 3 67. 4 (l) Percent acid absorption77. 0` 67. 0 (l) Aniline point, F 32 50 (l) .x l See Table II.

iIn` column 3 there are indicated the gravity, disare indicated thegravity, range of boiling point and other characteristics obtained fromthe dehydrogenation of the material shown in columnA 2.

Upon the accompanying drawing which forms a part of the instantspecification and which is to be read in conjunction therewith, there isplotted percentage overhead againsttop tower temperature in degreescentigrade, the curve identified by the letter A indicating the olefincontent,` curve 13, the specific gravity, and curve C, the top towertemperature.

The specific gravity of overhead cuts, each representing 1% of thecharge, was determined at centigrade. The curve exhibits a number ofmaxima and minima, behavior characteristics of cuts obtained byfractionating mixtures containing hydrocarbons of various types. Theolefin content of each 0.5% cut was determined by measuring the bromineabsorption. It is significant to note that in the lower temperatureregion olefin content varies inversely with specific gravity, that is,maxima in olen content corresponding to minima in the specic gravitycurve and vice versa.

By the simultaneous consideration of tower top temperature, specificgravity and olen content it is possible to obtain an approximation ofthe types of hydrocarbons present in a given cut. All three curves, A,B, and C, are plotted upon a single chart to facilitate simultaneouscomparison, each curve showing the variation of but one property at theparticular percent oi.

It will benoted that at the start 0f the distillation (i. e., up to 4%overhead), temperatures and specic gravity mount rapidly, while olefincontent declines. It is believed that this represents a gradual changein the overhead cuts from highly olefinic to highly aromatic content.The rst minimum in the specific gravity curve is probably attributableto a cut rich in benzene. Between the first and second peaks in speciiicgravity there is a second maximum in the olerln content curve (7% oil).This again is due to a highly unsaturated fraction, but the specificgravity, although at a minimum is still high (0.77), showing that theAolens present belong to the cyclic series. In this range, all oleiins ofthe usual type (e. g., the heptenes) have specific specific gravity(0.80).

tillation range, and other characteristics of a product resulting fromthe hydrogenation of the ,gravities of only 0.69 to 0.72, but cyclicolens have specific gravities in the neighborhood of 0.80. It is evidentthat the highly olefinic cut at approximately 7% oif consists largely ofcycloolens. The second specific gravity peak (10% off) is attributed toa toluene-rich product. Immediately beyond this is a third olei'ln peak,practically coincident with a minimum but high Olens (in the usualsense) of this boiling range have gravities of 0.70 to 0.73, so hereagain the olens present must be largely oi' a, cyclic nature.

The same reasoning can be applied throughout the distillation range butobviously the analysis becomes increasingly complex as the percentageoverhead increases. It is, however, a warranted conclusion that thisdistillate consists largely of cyclic compounds (aromatics, cyclo--unchanged, while the aromatics are also changed to naphthenes. It isobvious that if a highly aromatic nal product is desired hydrogenationis not the preferred procedure; while the hydrogenation conditions maybe so regulated that little or no aromatics are destroyed yet it isobvious that aromatics cannot be increased by this procedure.

On the other hand, if the above mixture is dehydrogenated, thecyclo-olefins and` naphthenes are readily converted to aromatics, whilethe aromatics themselves remain unchanged. By thisv latter procedure thequality of the distillate is improved, While by hydrogenation at best itremains constant. Results obtained from the eiect of hydrogenation on a70% overhead cut topped from this distillate, characteristics of whichare shown in column 1, are found in column 3 of the table. The 70%overhead cut shown in column 2 contains 90% of olens by bromineabsorption, but only 77% of olens and aromatics by acid absorption,indicating that an appreciable part of the olens present are diolens,and from the previous statements these must be largely cyclo-diolefins.

'Ihe 70% overhead material or product of column 2 was catalyticallyhydrogenated at 200# and 485 F. with a resultant product as shown` incolumn 3 of the tabulation. Inspection will show that the olen contenthas been reduced considerably by hydrogenation, while the aniline pointis increased, indicating that the suit Y of the samples obtained overthe period of 2.5-5

revivification will depend upon the rapidity of catalyst poisoning. Forcomparison of the results obtained on hydrogenation and dehydroabilityof the material for high solvency naphtha has been lowered. Byadjustment of conditions it might be possible to hydrogenate the stockwithout destroying appreciable aromatics,

The same material, namely, that of column 2 of the tabulation, wascatalytically dehydrogenated at 932 F. and atmospheric pressure in tworuns of five hours duration. While this specific temperature is given(932 F.), the invention contemplates as well a range of tempera- .tureof from 850 F. to 1200 F., a normal operating range being between 900 to1000 F. The products of each run were collected in two parts,

.representing 2.5 hours on stream, and 2.5-f5

hours. -An inspection and comparison of the four samples can be madefrom the following tabulation:

TABLE II Dehydrogenatiou of 70% overhead First run Second run Chargehrs. hrs. hrs. hrs.

Gravity, A. P .I 34. l 36. 5 35. 6 35. 6 35. 2 Percent oleiins 90. 3 66.4 78. 5 67. 0 76.0 Percent acid absorption. 77.0 77. 0 77.0 77.0 77.0Anilinepoint, "F 32 23.5 25.5 19.0 24.5

be noted that olen content and aniline point genating the dehydrogenatedproduct under as' genation the same catalyst was used.

A subsequent hydrogenation step in the presence of a catalyst may beadded as a step to supplement the dehydrogenating step and furtherconvert or remove any residual olens. This additional step ofhydrogenation is optional as indicated in the first example explained.

From the foregoing, it will be apparent that the instant invention liesin the discovery that a mixture of hydrocarbons containingaromatics andcyclo-olens may be subjected to dehydrogenation by any appropriatemethod to accomplish two results, namely,

(a) destroy the cyclo-olens,

(b) form aromatics.

The instant invention does not lie in a new method of dehydrogenationper se, but in the discovery that dehydrogenation may be applied to aparticular type of hydrocarbon to accomplish unobvious and usefulresults. Previous investigators have tried to obtain an aromaticcontaining mixture free from oleiins by hydrogenating the olens. It willbe clear from the foregoing that this is an ineffective and undesirablemethod. If, after the dehydrogenation, the residual oleiin content isstill too high, a mild hydrogenation may be practiced upon the resultantproduct to remove residual oleflns, if desired.

It will be understood that certain features and sub-combinations are ofutility and may be em- -ployed without reference to other features andsub-combinations. This is contemplated by and 'limited to the specicdetails shown and described.

Having thus described my invention, what I claim is:

1. A method of producing hydrocarbons rela tively free of olens andhaving a high aromaticI content which comprises cracking high boilinghydrocarbons in the presence of added normally gaseous-hydrocarbons,thereby producing a naphtha fraction rich in aromatics and containingolenic constituents largely in the form of cyclo-olens of six or morecarbon atoms, contacting said fraction with a dehydrogenation catalystat a temperature between 850 to 1200 F. at sustantially atmosphericpressures thereby decreasing the olenic content and increasing thearomatic content of the fraction, and catalytically hydromild conditionsas possible consistent with substantially complete hydrogenation ofresidualolefins.

2. A method of producing hydrocarbons relatively free of olens andhaving a high aromatic content which comprises cracking gas oil toproduce a fraction relatively rich in aromatics and cyclo-olefins of sixor more carbon atoms by atomizing the gas oil into hot combustionproducts of normally gaseous hydrocarbons, separating the fraction richin aromatics from the relatively heavy bottom fraction, contacting theseparated fraction with a dehydrogenation catalyst at a temperaturebetween 850. to 1200 F. at substantially atmospheric pressures therebydecreasing the olenic and increasing the aromatic content of thefraction, and catalytically hydrogenating the dehydrogenated productunder as mild conditions as possible consistent with substantiallycomplete hydrogenation of residual oleins.

3. A method of producing hydrocarbons relatively free of oleiins andhaving a high aromatic content, which comprises cracking naphtha in thepresence of recycled Ca and C4 hydrocarbons formed during the crackingreaction thereby producing a hydrocarbon fraction rich in aromatics andcontaining olefins largely in the form of cyclo-olefins of six or morecarbon atoms, contacting said fraction rich in aromatics with adehydrogenation catalyst at a temperature between 850 to 1200 F. atsubstantially atmospheric pressures thereby decreasing the olefinic andincreasing the aromatic content of the fraction, and catalyticallyhydrogenating the dehydrogenated product under as mild conditions aspossible consistent with substantially complete hydrogenation ofresidual olefins.

f ROBERT F. RUTHRUFF.

